Setting- Alternate universe w/o any super powered buddies (especially Manhattan). Vietnam war; Frank Castle and Eddie Blake are the last remainig survivors of their platoon.
Their mission; to capture a pivotal village suspected of trafficking arms. After all the original bad guys are taken care of, Castle takes a moment to himself to finish writing a letter to his wife and kids.
Not long after his first paragraph is he interrupted by the screams of a local village girl as she tries to keep the Comedians' sexual advances at bay. Castle quickly rushes to her aid, tackling Blake and smashing through a thin wooden wall into a large armament cache room.
The mood is set, and only one of these two is ever going to set foot on American soil again...
Special note; The attempted rape was primarily fabricated as a plot device to initiate conflict, so if you MUST argue that Castle has added momentum because of his personal beliefs, please estimate that Blake is just as pissed that he was interrupted in the first place.